Migraine headaches occur in approximately 12% of the world population. Therefore, in the United States in the year 2000 there are approximately 30 million people who suffer from this affliction. Although medicines have been created that significantly diminish the suffering of migraine patients, the medicines often have highly undesirable side effects and many patients do not obtain satisfactory relief from the severe headache pain and other discomforts associated with migraine. Furthermore, migraine headaches are typically treated after they have become painful, i.e., the treatment is often ineffective in preventing the onset of the migraine headache. Other than some drugs for some patients, there is no known treatment for migraine headaches that can be applied after a patient detects an aura of that headache to prevent the occurrence of pain and other undesirable manifestations of that migraine headache. A non-invasive, non-drug method for preventing the occurrence of migraine headaches would be a remarkable boon for those millions of people all over the world who suffer from these painful experiences.
In 1985, A. T. Barker, et al (Lancet, 1985, pp. 1105-1107) described the use of a coil placed over the scalp which produced a high intensity, time varying, magnetic field. This magnetic field produces an electric current in the cortex of the human brain which can in turn produce certain effects on brain neurons. By the year 2000, this type of system was given the name Transcranial Magnetic Stimulation (TMS). If repetitive magnetic pulses are applied in this manner, it has been given the name rTMS.
In the journal Neurology (Apr. 11, 2000, pp. 1529-1531) it has been reported by B. Boroojerdi, et al that rTMS at a rate of one pulse per second can create a reduction of the excitability of the neurons of the human visual cortex. However, no prior art has indicated that rTMS can be used for the preventing the occurrence of migraine headaches.
This invention is a means and method for the treatment of migraine headaches for those patients who experience a distinct aura before the actual occurrence of the symptoms of the migraine headache. It is estimated that approximately 40% of all migraine patients have a distinct aura that is a precursor of a migraine headache. Approximately half of these patients have a visual aura that typically begins as a small pattern of scintillating colored lights that have the appearance of wiggling worms. Over a time period of between 20 and 30 minutes, the pattern enlarges until it occupies nearly the entire visual field. During this time period, the patient might also completely lose part of his visual field. At the end of this visual aura, most migraine patients have a severe headache that is often accompanied by other symptoms such as nausea, vomiting and other unpleasant feelings. Many migraine patients who don""t have a visual aura have some other precursor of a migraine that can be perceived from minutes to hours before the actual start of the headache.
The visual aura is a result of the spatial progression of a band of brain cells that are excited in that band across one half of the brain""s occipital lobe. This band moves in an anterior direction at the rate of approximately 2-5 mm per minute. It is this excited band of neurons of the brain that produces the scintillating colored lights that are perceived by the patient as an aura that is a precursor of a migraine headache. Behind this leading band of excited neurons, a spreading region of neurons with depressed electrical excitability occurs. This phenomenon is known as xe2x80x9cthe spreading depression of Leaoxe2x80x9d.
It is believed that if the advancing band of excited neurons can be stopped before the aura has completed its 20 to 30 minute time duration period, the migraine headache will not occur. One way to stop such an advancing band of excited brain neurons would be by imposing a high enough electric current through these neurons so that they become depolarized. This could be accomplished by means of electrodes placed on the brain""s surface at the occipital lobe (i.e., the visual cortex). If these electrodes would have at least several milliamps of electrical current placed across them, the excited neurons could be depolarized, thus eliminating their enhanced excitability. However, this would require surgery to implant such electrodes. Also, a neurostimulator attached by wires to the electrodes would be required, which neurostimulator would be adapted to place a voltage across the electrodes to cause the flow of a sufficiently high electrical current to depolarize the advancing band of excited neurons.
The invention disclosed herein is a non-invasive, externally applied device that is placed on or near the patient""s head in the region of the brain where the aura originates (e.g., the occipital lobe) as soon as possible after the patient becomes aware of a visual (or any other type) aura that is a precursor of the migraine headache. For patients whose aura originates from a region of the cerebral cortex that is not the occipital lobe, the depolarizing device can be applied to that region of the brain. By the use of a high intensity alternating magnetic field, a sufficiently high electrical current can be placed onto the advancing band of excited neurons so as to depolarize those neurons thereby terminating the aura before it is able to progress into a migraine headache. Depolarization of neurons in advance of the advancing band of excited neurons may also be used to prevent a migraine headache. This is because depolarized neurons become refractory after rTMS is applied. This is analogous to cutting down or burning the trees in front of a forest fire in order to prevent the spread of that forest fire.
The one pulse per second of rTMS described by Boroojerdi, et al, which was proven to cause a reduction of cerebral cortex excitability, could be applied to break up the advancing band of excited neurons that is the cause of the visible aura of a migraine headache. Since an aura has a time duration that is typically at least 20 minutes, the patient has a sufficient time period for placing the rTMS magnetic depolarizer in the appropriate position for it to be effective in depolarizing the advancing band of excited brain neurons.
It should also be noted that stimulation of the scalp might also have an effect in preventing or decreasing the severity of a migraine headache for at least some patients. Scalp stimulation may act as a conditioning, response that becomes associated with the migraine process. Pairing this response with rTMS may provide cessation of the migraine process with progressively less intensity of magnetic stimulation.
Since the band of excited neurons that create a visual aura moves from the back of the head in an anterior direction, and since either the left or right half of the occipital lobe might be involved, the magnetic depolarizer would optimally be placed along the posterior-anterior centerline at the top of the head. If it is known that a particular patient has the spreading depression on either the right or the left half of the occipital lobe, then the magnetic depolarizer might be placed only on that region where the spreading depression occurs. If the aura originates from a part of the cerebral cortex that is not the occipital lobe, then the alternating magnetic field can be appropriately placed to depolarize neurons in that location. It is expected that the patient can be trained to recognize the symptoms from a particular area of the brain so that the magnetic depolarizer can be placed in an optimum location to prevent the occurrence of a migraine headache.
The magnetic depolarizer can be formed in a race-track, figure-eight shape with its long axis placed along the head""s posterior-anterior centerline. The width of the magnetic depolarizer might be between 1 and 10 cm and its height in a direction above the skull could be between 0.5 to 5 cm. The length of magnetic depolarizer would typically be between 3 and 15 cm. The magnetic depolarizer could be placed within some form of head covering such as a bicycle helmet. A rechargeable battery and electronic circuitry to generate the required alternating magnetic field could also be contained within a helmet type of head gear. A conventional A-C adapter (recharging device) could be provided to the patient for recharging the battery of the magnetic depolarizer system.
A sufficiently intense alternating magnetic field must be created that would cause the excited band of brain neurons to be depolarized before this band has a chance to create a migraine headache. The intensity of the magnetic field at the surface of the brain should be between 0.1 and 10 Tesla. The frequency rate of the magnetic pulses should be between 0.1 Hz and 1.0 kHz. With some patients a single, short duration pulse may be all that is required to stop an advancing band of excited neurons from proceeding to a full-blown migraine headache. The magnetic pulses can be applied continuously for a period of between 0.1 and 100 seconds. By applying a time varying magnetic field to the neurons of the cerebral cortex (and also to the neurons in the scalp), a patient could be able to actually prevent the occurrence of a migraine headache.
Thus, an objective of this invention is to prevent the occurrence of a migraine headache by creating a high intensity, time varying magnetic field by means of a magnetic depolarizer placed onto the scalp of a patient who has an aura which is a precursor of a migraine headache, the magnetic depolarizer being adapted to cause depolarization of the neurons in the cerebral cortex where the aura originates.
Another object of this invention is to have the magnetic depolarizer placed inside a headgear that the patient can place on his or her head, the headgear being adapted to place the magnetic depolarizer at a specific location relative to the patient""s cerebral cortex.
Still another object of the invention is to have a magnetic depolarizer system that includes a battery, electronic circuitry (including a magnetic depolarizer) for creating a high intensity, time varying magnetic field, a patient operated ON-OFF switch and settings of the system""s operating parameters that are set by a physician.
Still another object of the invention is to have the magnetic depolarizer system use a rechargeable battery.
These and other objects and advantages of this invention will become obvious to a person of ordinary skill in this art upon reading the detailed description of this invention including the associated drawings as presented herein.